1. Field of the Invention
The present invention relates to electrochromic display devices of the liquid electrolyte type. More particularly, the present invention relates to electrochromic display devices of the liquid electrolyte type having a persistent electrochromic effect.
2. Description of the Prior Art
It is known that an electrochromic display may be produced by the passage of electric current through an electrolyte. In solid electrolytes, an electrochromic effect is due to color center absorbing species produced by electrochemical reaction. In liquid electrolytes, the electrochromic effect is due to the deposition of a colored species on one of the electrodes. In known electrochromic displays of this kind, the display electrodes, i.e., the electrodes on which species is deposited to produce the required display, are associated each with a counter electrode at which the opposite electrochemical reaction takes place. Typical of electrochromic display devices and their operating characteristics are those described by I. F. Chang et al in "Performance Characteristics of Electrochromic Displays" appearing in IEEE Transactions on Electron Devices, ED 22, No. 9, Sept. 1975, pp. 749-758.